1. Field of the Invention
The present invention relates to an occupant restraint apparatus for restraining an occupant within an interior side by covering an interior side of a window of a vehicle.
2. Related Art
Conventionally, in an airbag system including a head protecting airbag which is adapted to be completely inflated so as to cover an interior side of a window of a vehicle, the inflation of the airbag is completed whereupon a tensile force (tension) is generated to be exerted along a longitudinal direction so as to restrain an occupant of the vehicle (refer to, for example, Japanese Patent Publication No. JP-A-10-278723).
Such a tension is generated by providing a plurality of cells within the airbag so as to be juxtaposed in the longitudinal direction to narrow the longitudinal dimension of the airbag to be inflated when an inflating gas is introduced thereinto for completion of the inflation of the airbag and attaching a front end lower portion and a rear end upper portion of the airbag to a lower portion of a front part and a rear portion of an upper part of the window, respectively. Note that the plurality of cells not only function to generate the tension but also contribute to helping the completely inflated airbag to maintain its plate-like shape which extends along the inside of the compartment.
Then, when a tension is generated by the plurality of cells juxtaposed in the longitudinal direction which is exerted along the longitudinal direction of the airbag, even in case the occupant is force to be out of the compartment, the airbag can restrict the outward movement of the occupant so as to restrain the occupant within the compartment.
In the conventional airbag, however, since the front end lower portion and rear end upper portion of the airbag are attached to the lower portion of the front part and the rear portion of the upper part of the window, respectively, while a tension is generated along a line extending upward from the front end lower portion to the rear end upper portion of the airbag when the airbag has been fully inflated for complete deployment, a tension cannot be generated along a part itself which connects the front end lower portion to a rear end lower portion of the airbag when it has been fully inflated for complete deployment or along a lower edge itself of the airbag which extends in the longitudinal direction thereof when the airbag has been fully inflated for complete deployment, and hence there still remains a room to be improved with respect to the performance for restraining the occupant within the inside of the compartment.
Incidentally, while it is considered that the front end lower portion and rear end lower portion of the airbag are both fixed to the side of lower portions of the front and rear parts of the window, in this state, when the airbag is folded to be housed on the upper part of the window, since the longitudinal length of the airbag along the lower edge thereof is not sufficiently long, the housing becomes impossible. On the contrary, in the event that the longitudinal length of the airbag along the lower edge thereof is excessively long, while the airbag can be housed in the upper part of the window, the airbag cannot provide sufficient tension in the lower edge along the longitudinal direction thereof, even when the plurality of cells are inflated.
In addition, in the conventional airbag, since the tension is generated on the lower edge of the airbag by inflating the plurality of cells which are juxtaposed in the longitudinal direction of the airbag, in the event that a situation is called for in which the cells are damaged in association with the roll of the vehicle on to its side, causing a leakage of the inflating gas, whereby the internal pressure of the airbag is reduced, the tension cannot be maintained.